There has conventionally been an authentication apparatus that authenticates a user by using a fingerprint. Specifically, fingerprint data related to a fingerprint of a user is registered beforehand to the authentication apparatus. For example, image data of a fingerprint is preliminarily stored in the authentication apparatus, or data involved with characteristic points contained in a fingerprint is preliminarily stored in the authentication apparatus. During the authentication, the authentication apparatus acquires fingerprint data from the user, and compares the fingerprint data to the fingerprint data preliminarily stored, thereby authenticating the user. When the authentication apparatus fails in authenticating the user in one authentication process, it acquires again the fingerprint data from the user, and executes again the authentication process by using the acquired fingerprint data, for example. The authentication apparatus continues to acquire the fingerprint data from the user until it succeeds in authentication.
There is an authentication apparatus that increases or decreases FAR (false acceptance rate) during the authentication based upon a number of times of acquiring the fingerprint data until the apparatus succeeds in authentication. For example, when the number of times of acquiring the fingerprint data is not less than a threshold value, the authentication apparatus that increases or decreases the false acceptance rate increases the false acceptance rate used for the subsequent process. Increasing the false acceptance rate means that the possibility of falsely recognizing a person who should not be recognized becomes high. In other words, when the false acceptance rate increases, the accuracy in the authentication is deteriorated.
There is also an authentication apparatus that sets a number of fingers used for the authentication or the false acceptance rate based upon the condition of the finger, when the fingerprint data is registered. For example, for a person having a satisfactory finger's condition, the authentication apparatus that sets the number of fingers sets that two fingers are used, and sets the false acceptance rate that is smaller than that for a person having unsatisfactory finger's condition, and when the fingerprint data preliminarily registered and the fingerprint of one finger coincide with each other, it determines that the authentication is successful. For a person having unsatisfactory finger's condition, the authentication apparatus that sets the number of fingers sets that three fingers are used, and sets the false acceptance rate that is larger than that for a person having satisfactory finger's condition, and when the fingerprint data preliminarily registered and the fingerprint of three fingers coincide with each other, it determines that the authentication is successful. The authentication apparatus authenticates the user during the authentication by using the number of fingers or the false acceptance rate set upon the registration.
Patent Document 1: Japanese Laid-open Patent Publication No. 2000-011179
Patent Document 2: Japanese Laid-open Patent Publication No. 11-096358
However, the authentication apparatus that increases or decreases the false acceptance rate entails a problem of deterioration in authentication accuracy. Specifically, when the number of times of acquiring the fingerprint data is not less than the threshold value, the authentication apparatus that increases or decreases the false acceptance rate decreases the false acceptance rate, which deteriorates the authentication accuracy.
The authentication apparatus that sets a number of fingers entails a problem of deterioration in operability when the condition of the finger during the authentication is different from the condition of the finger during the registration. Specifically, when the condition of the finger is deteriorated compared to the condition during the registration, the authentication apparatus that sets the number of fingers does not succeed in the authentication even with the false acceptance rate set during the registration. In other words, the apparatus falsely recognizes that a normal user is not a normal user. Thus, the operability is deteriorated.
When the condition of the finger is enhanced compared to the condition during the registration, the authentication apparatus that sets the number of fingers applies extra load to the user. For example, the case where the apparatus sets that three fingers are used during the registration, but only one finger is enough during the authentication will be described. In this case, the authentication apparatus that sets the number of fingers acquires fingerprint data from three fingers, although it is only enough to acquire the fingerprint data from one finger. In other words, extra load is applied to the user, which deteriorates operability.